The list of electroactive medical devices is growing by the day. The list includes electroactive Intra Ocular Lenses, pacemakers, implantable drug delivery systems, neuro-stimulators, in-vivo sensors, and medical devices with rechargeable batteries.
A substantial fraction of these electroactive medical devices include an integrated, or on-board, battery to energize their on-board electronics. For implantable medical devices, rechargeable batteries are used that can energize the medical device until they are depleted, at which time they get recharged to keep the medical device operational.
Rechargeable batteries, just like all batteries, start losing their charge and thus the energy they store, once the charging is finished. There are several advantages of compensating this “self-discharging” process and keeping the charging state of the batteries of the medical devices sufficiently high after their manufacture.
One of the leading reasons is that the performance of wide classes of batteries exhibits accelerated degradation, if the self-discharging is allowed to become excessive, and the batteries' charging state is allowed to drop significantly below a lower threshold. After such an excessive self-discharge, the batteries cannot be recharged to the same energy level anymore because of irreversible electro-chemical reactions: the energy storing capacity of the batteries exhibits degradation. Such degraded batteries require recharging more frequently, and can operate only for shorter periods between recharges. Both these factors affect their functionalities negatively. Further, often the overall usable lifetime of such excessively self-discharged batteries also shrinks.
Second, a substantial time period can elapse between the manufacture of the battery of the medical device, and the implantation of the device into a patient. In this period, the self-discharging can lead to the loss of a substantial fraction of the energy stored in the battery, thus reducing the time before the battery needs recharging after implantation, possibly even rendering the implanted medical device non-operational after implantation.
For all these reasons, there is a need to compensate the self-discharging of the integrated on-board batteries of implantable electroactive medical devices between their manufacture and their implantation by keeping their charging state above a lower threshold.
Some simple solutions turn out not to be particularly workable. For example, it can be attempted to overcharge the on-board battery at the time of its fabrication, so that even after the self-discharge, its charging state remains above a lower threshold. However, such overcharging above an upper threshold can lead to a performance degradation that is comparable to the performance degradation caused by the charging state decaying below the lower threshold.
A battery manufacturer and a device manufacturer can also advise the ophthalmic surgeons to implant the devices within a short time period after the manufacture of the batteries. However, the overall distribution process is not within the control of the device manufacturer, since the sale of the device may take longer than expected, or the surgeon may store the medical device after its purchase for a period longer than desirable. Without controlling the intermediary process, the medical device manufacturer cannot provide the required guarantees about the performance of its product devices.
Finally, a periodic charging-state-monitoring protocol can be required by intermediary custodians of the medical device after its manufacture, such as a human monitor checking the charging state of the batteries manually and periodically at the intermediate stops of the distribution process, including in medical warehouses, in transit, and in hospital storage facilities. However, this approach is subject to human error, is labor intensive, and requires operating a substantial human workforce, resulting in considerable overhead costs.
For all the above reasons, new solutions are needed to compensate the self-discharging of on-board batteries of electroactive medical devices between their manufacture and the implantation of the electroactive medical device.